1. Field of the Invention
The present invention relates to etching systems for etching objects such as metal films deposited on glass substrates used in liquid crystal displays, and particularly to an etching system using a deionized water (DIW) adding device.
2. Description of Prior Art
In the production of a typical thin-film transistor liquid crystal display (TFT LCD), an indium tin oxide (ITO) film deposited on a glass substrate needs to be etched, so as to cut away unwanted ITO material and leave a final desired ITO circuit pattern. Generally, oxalic acid is used as the etchant to etch the ITO film. To regulate and stabilize the concentration of the oxalic acid solution, DIW needs to be added to the solution at appropriate times and in appropriate quantities. Accordingly, a DIW adding device performing this function is used in the etching process.
Referring to FIG. 3, this shows a schematic, side plan view of a conventional etching system 1. The etching system 1 comprises an etching chamber 11, an etchant solution tank 12, an etchant solution feeding pipe 14, and a DIW feeding pipe 13 having a timer 131. The etchant solution tank 12 is filled with an etchant solution (not labeled) such as an oxalic acid solution. The etchant solution generally is heated by a heater (not shown) to a predetermined temperature.
In operation, a pump (not shown) drives the etchant solution from the tank 12 through the etchant solution feeding pipe 14 into the etching chamber 11. Etching is carried out on a workpiece such as a glass substrate in the etching chamber 11. The timer 131 controls opening and closing of the pipe 13. Thus the DIW is added into the etching chamber 11 at appropriate times and in appropriate quantities to stabilize the concentration of the etchant solution in the etching chamber 11.
However, the etching chamber 11 generally is connected with other chambers (not shown) which are used for processing the etched glass substrate. A reactant gas such as an acidic gas occurring in the process of the etching work may easily flow into the other chambers. Similarly, etchant solution adsorbed and held by surface tension on the glass substrate may easily be carried into the other chambers. The reactant gas and the etchant solution may impair the processing of the glass substrate in a next step in another chamber.
Referring to FIG. 4, this shows another conventional etching system 2. The etching system 2 comprises an etching chamber 21, an etchant solution tank 22, an etchant solution feeding pipe 26, a DIW feeding pipe 23 having a timer 231, and a clean dry air (CDA) feeding pipe 24 having a timer 241. The two pipes 23, 24 combine into a main pipe 25. The timers 231, 241 respectively control the pipes 23, 24 to open at different times to feed DIW and CDA alternately.
The pipe 24 feeds CDA into the etching chamber 21, so that any reactant gas in the etching chamber 21 is diluted and effectively eliminated before it can flow into the next chamber. The CDA also blows off the etchant solution held on the glass substrate.
The CDA and the reactant gas at the end of the main pipe 25 in the etching chamber 21 flow intensely, and this is where certain mechanisms (not shown) of the etching chamber 21 are located. As a result, etchant solution located on the mechanisms near the end of the main pipe 25 crystallizes easily. The crystallized etchant solution can hamper the movement of the mechanisms. Therefore the DIW feeding pipe 23 feeds DIW to dissolve and remove the crystallized etchant solution.
The etching system 2 has the following disadvantage. The DIW fed by the pipe 23 is generally at room temperature, while the temperature of the etchant solution in the etching chamber 21 is higher than room temperature. Thus when the DIW is fed into the etching chamber 21, the temperature of the etching chamber 21 fluctuates, which can reduce the accuracy and efficacy of the etching being carried out.
Thus, a new etching system which overcomes the above-mentioned disadvantage is desired.